This story is a sequel to Lines and Webs

For four long years, Celestia's apprentice Twilight Sparkle, once a model pony and a hero among heroes, has waged a bitter and secret struggle with her onetime mentor. Though she works from the shadows, directing her forces from the Old Capitol in the Everfree Forest, Twilight Sparkle is unable to gain any advantage,

Likewise, Princess Celestia finds her once-faithful student far more cunning and elusive than she had anticipated, and even now searches for a way to bring Twilight Sparkle's rebellion to its knees.

It is a game of greys, of knives in the dark and of poisoned wine, where pawns are moved and traded and exchanged for greater advantage, all the while drawing both sides nearer to the conflict which shall tear Equestria in two.

At the center of this conflict is a new pawn, one who only wished to see the truth for herself. Drawn into a deadly game whose rules she does not understand, Sweetie Belle must learn to survive in a world where all is darkened, and nopony can be completely trusted.

Because when gods play chess, all pieces are expendable.

A nation will crumble, old enemies shall return in the most unexpected ways, and regardless of who is victorious, only one thing can be certain.

Nothing shall ever be the same.

Followed by Stormsinger.

It has been ten years since the defeat of the Changling Queen, and Equestria is again at peace. Twilight Sparkle and the Elements of Harmony have reached their prime, and have begun to settle down. Love and life abound in Ponyville, especially for Twilight's friends, but she has nopony to call her own.

There is a reason.

A series of events lead to a horrible revelation, and Twilight is thrust deep into a terrifying web of secrets and lies. Her peace is over.

This time, however, she won't be fighting monsters or madponies. What she faces will be much, much worse.

Act One of Two.

Act Two is here.

Currently undergoing editing by the wonderful Mstar!

Twilight Sparkle broke time when she got her cutie mark. Now Twilight and Sparkle are sisters from another time. Twilight is hailed as the potentially greatest light magician of all time, and already has a reputation as a hero by the time she goes to Ponyville. This isn't her story, not primarily.

Sparkle is an orphan - her dark magic killed her parents. She lives with her brother in Canterlot's industrial sector because they can't afford anything better. She can't leave either. She's a natural dark mage; while Sparkle won't go mad like Sombra, her reputation is hardly any better. Worse, the law doesn't see her as a good pony.

The fact that the dead don't stay dead around her, or that Thorn - Spike's double - is an undead, soul-eating abomination, are other matters altogether.

(Also has some Slice-of-Life, but fimfiction tags won't let me put it with Adventure.)

Has an ask blog to go with it: Ask Sparkle and Thorn.
Also has a TvTropes page: Split Second Tropes.

Featured on EQD.

Cover art by Swirling Line.

This story is a sequel to Project: Sunflower

After the events of Project: Sunflower, Erin Olsen has returned to Ponyville, happy to pursue her studies in magic. After everything that happened the year before, she's looking forward to spending her days studying and having fun with her friends.

Meanwhile, on the newly discovered world of Harmony, humans and ponies work together to study this strange new world. However, their arrival causes something ancient to begin stirring. Something that may end up changing everything.

Erin will need all of her courage, all of her cleverness and, of course, all of her friends to see herself through what happens next.

Cover art by Valkyrie-Girl
Editing provided by:
Brilliant Point, Coandco, Ekevoo, Ludicrous Lycan, Merlos the Mad and Razalon the Lizardman.

It is the year 2038, and the Earth is slowly being consumed by a space-borne monstrosity dubbed the Black Tide, which is using nanotechnology to remake the planet into something hideously alien.

Erin Olsen works for Project Harmonics, humanity's last-ditch effort to find a new world before the Tide can wipe them out. But when that world is found, and it turns out to be occupied, Erin will need to find the courage to face the unknown in order to save the inhabitants of both worlds.

(Many thanks to Easteu for the fantastic cover image for this story!)

Now with its own TV Tropes page

There is now a follow-up to this story: Sunflower - Side Projects
Sequel: Project Sunflower: Harmony

Talks broke down. The unification failed. Hearth's Warming have never occurred. The Great Pony War divided the land, and fears of a prophecy forced the unicorns deep underground and into near extinction.

Almost one thousand years have passed. The curious unicorn Sparkle yearns to breach the surface to discover its many wonders and to search for her missing father and brother, both of whom crossed over many years ago. She is forbidden to leave the safety of her subterranean village of Unicornia until she discovers an orange earth pony washed up on the shores of an underground river. That pony bears one of the six Elements fabled to change the world.

Or destroy it.

Cover art credit goes to ouyrof.

Re:Harmony was conceived before Season 4 aired, so some personalities and character relations do not line up with the show's canon.

Also, please refrain from revealing spoilers in the comments. Thanks!